Measuring laser light transmissivity in a to-be-welded region of a work piece

ABSTRACT

Methods for measuring laser light transmissivity of a specific position in a work piece prior to the work piece undergoing laser welding at the specific position with a laser beam having a specific welding wavelength. To obtain a baseline measurement reading, a laser light source projects a laser beam at the welding wavelength directly into a detector. Thereafter, the work piece becomes suspended between the laser light source and detector whereby an output of the detector now corresponds to a work piece measurement reading. Differences between the two readings reveal whether the work piece will yield a satisfactory weld at the specific position when later welded by a laser beam at the welding wavelength. Preferred work pieces include inkjet printhead lids and bodies.

FIELD OF THE INVENTION

[0001] The present invention relates to measuring light transmissivityof a work piece. In particular, it relates to measuring laser lighttransmissivity of a specific position in a work piece prior to the workpiece undergoing laser welding at that specific position. Even moreparticularly, it relates to assessing whether the work piece will yielda satisfactory weld at the specific location when welded by a laser beamirradiated at a specific welding wavelength. Work pieces may compriseinkjet printhead lids and bodies.

BACKGROUND OF THE INVENTION

[0002] The art of measuring light transmissivity in a work piece isrelatively well known. In general, light from a source passes from afront side of the work piece to the backside where a detector collectsit. The difference between the light irradiated towards the work pieceand the light that actually passes through the work piece, as collectedby the detector, corresponds to the work piece transmissivity.

[0003] Problems arise, however, because the light source, often a whitelight source, illuminates the front of the work piece with multiplewavelengths while the detector only collects light at its tunedwavelength. This can unnecessarily limit measurement of multiplewavelengths to incorporating multiple detectors. Additionally, typicalcommercial transmissivity measurement devices lack sufficientirradiation power to penetrate work pieces and project light to backsidedetectors when the work pieces embody other than visibly clearcompositions. Traditional visibly clear compositions include glass,quartz, polycarbonate, polystyrene, and the like. They usually also lacksufficient power to project light through work pieces, such as highimpact polystyrene and polyester having typically low transmissivitycharacteristics.

[0004] Accordingly, the arts for measuring light transmissivity desiresolutions for overcoming the aforementioned and other problems.

[0005] Numerous reasons exist for understanding light transmissivity ina work piece. For example, consider instances when two work piecesundergo laser welding. As background, first and second work piecesbecome welded to one another by way of a fixed or sweeping irradiatedbeam of laser light. As is known, the beam passes through the first workpiece, which is transparent to laser light, where it gets absorbed bythe second work piece, which is laser light absorbent. As the beamirradiates, the weld interface heats-up which causes the adjoiningsurfaces of the work pieces to melt. Upon cooling, the two work piecesmeld together as one.

[0006] Yet, if the first work piece prevents sufficient amounts of laserlight from reaching the weld interface, poor welding (underweld)results. Further, if the first work piece absorbs too much energy, thefirst work piece may overheat and/or suffer material degradationpotentially causing poor weld appearance or unsatisfactory welds.Numerous parameters contribute to the absorption and transmissioncharacteristics of a work piece including, but not limited to, laserwavelength, incident angle of the laser beam during welding, surfaceroughness of the work piece, temperature of the work pieces,thickness/dimensions of the work piece, composition of the work pieceand, in instance when work pieces comprise plastics, additives such asflame retardants, plasticizers, fillers and colorants.

[0007] When the material properties and laser properties become fixed ina given system, however, the transmission rate of the laser through awork piece follows the well known Beer-Lambert Law, specifically:I/Io=e^((−sx)); where Io is the intensity of the light source incidenton the work piece, I is the intensity of the light after passing throughthe work piece, x is the thickness of the work piece, and s is the totalextinction coefficient which, in turn, is the work piece lightscattering coefficient plus the work piece light absorption coefficient.Accordingly, the transmissivity of the work piece constitutes animportant variable (underscored by the ratio I/I_(o)) in lighttransmission rates.

[0008] As such, those skilled in the laser welding arts will appreciatethat having an ability to assess, predict or otherwise identify a laserlight transmissivity characteristic of a work piece before the pieceundergoes welding will likely significantly decrease failure weld-ratesin to-be-welded work pieces.

[0009] Accordingly, a need exists in the laser welding arts forefficaciously predicting and identifying laser light transmissivity into-be-welded regions of a work piece.

[0010] Regarding the technology of inkjet printing, it too is relativelywell known. In general, an image is produced by emitting ink drops froman inkjet printhead at precise moments such that they impact a printmedium, such as a sheet of paper, at a desired location. The printheadis supported by a movable print carriage within a device, such as aninkjet printer, and is caused to reciprocate relative to an advancingprint medium and emit ink drops at such times pursuant to commands of amicroprocessor or other controller. The timing of the ink drop emissionscorresponds to a pattern of pixels of the image being printed. Otherthan printers, familiar devices incorporating ink-jet technology includefax machines, all-in-ones, photo printers, and graphics plotters, toname a few.

[0011] A conventional thermal inkjet printhead includes access to alocal or remote supply of color or mono ink, a heater chip, a nozzle ororifice plate attached to the heater chip, and an input/outputconnector, such as a tape automated bond (TAB) circuit, for electricallyconnecting the heater chip to the printer during use. The heater chip,in turn, typically includes a plurality of thin film resistors orheaters fabricated by deposition, masking and etching techniques on asubstrate such as silicon.

[0012] To print or emit a single drop of ink, an individual heater isuniquely addressed with a small amount of current to rapidly heat asmall volume of ink. This causes the ink to vaporize in a local inkchamber (between the heater and nozzle plate) and be ejected through andprojected by the nozzle plate towards the print medium.

[0013] During manufacturing of the printheads, a printhead body getsstuffed with a back pressure device, such as a foam insert, andsaturated with mono or color ink. A lid welds to the body via ultrasonicvibration. This, however, sometimes causes cracks in the heater chip,introduces and entrains air bubbles in the ink and compromises overallintegrity.

[0014] Even further, as demands for higher resolution and increasedprinting speed continue, heater chips become engineered with morecomplex and denser heater configurations which raises printhead costs.Simultaneously, the heater chips become smaller and flimsier to savesilicon costs. Thus, as printheads evolve, a need exists to controloverall costs and to reliably and consistently manufacture a printheadwithout causing cracking of the ever valuable heater chip.

SUMMARY OF THE INVENTION

[0015] The above-mentioned and other problems become solved by applyingthe principles and teachings associated with the hereinafter describedmeasurement of laser light transmissivity in a to-be-welded region of awork piece.

[0016] In one embodiment, the invention teaches methods for measuringlaser light transmissivity of a specific position in a work piece priorto the work piece undergoing laser welding at the specific position witha laser beam having a specific welding wavelength. As a first step, theinvention teaches obtaining a baseline measurement reading between alaser light source and a detector by projecting a laser beam, at theto-be-welded welding wavelength, directly into the detector. The workpiece becomes suspended between the laser light source and detector suchthat the laser beam at the welding wavelength passes through the workpiece in the vicinity of the specific to-be-welded position and into thedetector. An output of the detector corresponds to a work piecemeasurement reading. Differences between the two readings reveal whetherthe work piece will yield a satisfactory weld at the specific positionwhen later welded by a laser beam at the welding wavelength. Theinvention also contemplates filters, mirrors, collimators, lenses andthe like in the optical path between the light source and the detector.

[0017] In another aspect of the invention, a substantially bottomlesstray suspends work pieces between the laser light source and thedetector such that when the work piece becomes indexed to a newposition, the tray never interferes with the beam of laser light. An X-Ymotion table in combination with a stepper motor preferably provides theimpetus for indexing.

[0018] In still another aspect, indexing motion and laser lighttransmissivity readings occur in patterns substantially paralleling aperiphery of the work piece.

[0019] Inkjet printhead lids and bodies, laser welded together atspecific positions having undergone laser light transmissivitymeasurements at specific welding wavelengths, and printers containingthe printheads are also disclosed.

[0020] These and other embodiments, aspects, advantages, and features ofthe present invention will be set forth in the description whichfollows, and in part will become apparent to those of ordinary skill inthe art by reference to the following description of the invention andreferenced drawings or by practice of the invention. The aspects,advantages, and features of the invention are realized and attained bymeans of the instrumentalities, procedures, and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a diagrammatic view in accordance with the teachings ofthe present invention of an apparatus for measuring laser lighttransmissivity in a to-be-welded region of a work piece;

[0022]FIG. 2A is a diagrammatic view in accordance with the teachings ofthe present invention of a tray for suspending a work piece between alaser light source and a detector for use with the apparatus of FIG. 1;

[0023]FIG. 2B is a cross-section view in accordance with the teachingsof the present invention of the to-be-welded work piece of FIG. 2A afterbeing placed in the tray;

[0024]FIG. 2C is a planar view in accordance with the teachings of thepresent invention of the to-be-welded work piece held in the tray ofFIG. 2B having pluralities of laser light transmissivity measurementpositions indicated;

[0025]FIG. 3 is a diagrammatic view in accordance with the teachings ofthe present invention of laser light projected through a work piece andcollected by a detector for use with the apparatus of FIG. 1;

[0026]FIG. 4 is a graph in accordance with the teachings of the presentinvention of measured laser light transmissivity of a work piece plottedagainst discrete measurement positions;

[0027]FIG. 5 is a perspective view in accordance with the teachings ofthe present invention of an inkjet printhead with a laser lighttransmissivity measured inkjet lid laser welded to an inkjet body; and

[0028]FIG. 6 is a perspective view in accordance with the teachings ofthe present invention of an inkjet printer for housing an inkjetprinthead with a laser light transmissivity measured inkjet lid laserwelded to an inkjet body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] In the following detailed description of the preferredembodiments, reference is made to the accompanying drawings that form apart hereof, and in which is shown by way of illustration, specificembodiments in which the inventions may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, and it is to be understood that otherembodiments may be utilized and that process or other changes may bemade without departing from the scope of the present invention. As amatter of convention herein, direction arrows and lines in-between serveto show interconnections between devices. The following detaileddescription is, therefore, not to be taken in a limiting sense, and thescope of the present invention is defined only by the appended claimsand their equivalents. In accordance with the present invention, wehereinafter describe measurement of laser light transmissivity in ato-be-welded region of a work piece.

[0030] With reference to FIG. 1, an apparatus for measuring lighttransmissivity is shown generally as 10. The apparatus includes acomputing system environment 12 having, at one end thereof,bi-directional communication with a laser diode power controller 14 anda laser diode temperature controller 16. In a preferred embodiment, thepower controller embodies a Thorlabs Inc., LDC2000 2A laser diodecontroller while the temperature controller embodies a Thorlabs Inc.,TEC2000 TEC controller. The computing system environment embodies ageneral or specific purpose computer with attendant processors, memory,monitors, input devices, network connections, peripheral devices,application programs, connections to intranets and internets and thelike.

[0031] At the other end, the computing system environmentbi-directionally couples with a laser light source structure 20, amotion table 22 and a detector structure 24. In more detail, the laserlight source structure 20 includes a laser mount 26, a laser diode 28and collimating and focusing optics 30. In a preferred embodiment, thelaser mount includes a Thorlabs Inc., TCLDM3 TEC LD mount while thediode includes a 1200 mW, TO-3 package from Coherent Laser Diode,S-81-1200C-100-Q. The collimating and focusing optics comprise one orsome of Thorlabs Inc.'s: C230TM-B, 600-1500 nm Moderate NA Optics;C260TM-B 600-1500 nm 0.15 NA AR coating; E09 RMS Microscope ObjectiveAdapter Extension Tube; Optics Adapter S1TM09; CP02 Threaded Cage Plate;SM1A3 Microscope Objective to SM1 Adapter; ER4 0876-001 REV B, ExtensionRod 4 inch (×4); and SM1RR Retaining Ring. In other embodiments, thelaser diode represents an 810 nm wavelength aluminum gallium arsenide(AlGaAs) semiconductor laser having a laser power of about 1000 mW.Still other embodiments include, but are not limited to, other types ofcontinuous wave lasers with similar power intensities such assemiconductor lasers based on Indium Gallium Arsenide (InGaAs) withwavelengths of 940-990 nm and Aluminum Gallium Indium Phosphide(AlGaInP) with wavelengths of 630-680 nm, solid state lasers such aslamp pumped Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) with awavelength of 1064 nm and diode pumped Neodymium-doped Yttrium AluminumGarnet (Nd:YAG) with a wavelength of 1064 nm or solid-state, gas,excimer, dye, ruby or semiconductor lasers or argon fluoride, kryptonfluoride, nitrogen, argon (blue or green), helium neon (blue or green),rhodamine 6G dye (tunable), CrAlO₃, NIR or carbon dioxide (FIR) lasertypes or other. The laser diodes of the laser light structure mayadditionally have labels of class I, I.A, II, IIIA, IIIB, or IV as thoseare well understood in the art.

[0032] The motion table 22 has an elevation arm 32 that allows insertionof a work piece 50 into an optical path (dashed straight line betweenlaser and detector structures) at a position above the laser lightsource structure. An offset arm 34 of the motion table provides lateralcontrol with motion controlled in a region away (action arrow A) fromthe optical path. A microcontroller 36 and stepper motor 38 provide theelectrical and mechanical impetus to the motion table preferably frominstructions originating in the computing system environment. In oneembodiment, the motion table 22 has X-Y positioning. In otherembodiments, the motion table has X-Y-Z motion, theta motion, angularmotion, linear motion or combinations of some or all of the foregoing.

[0033] The detector structure 24 includes a photodetector 40 and anoptional filter 42. In one embodiment, the photodetector is a ThorlabsInc., DET 110 350-1100 nm Photodetector while the filter is an NE20AD-2.0 Mounted Absorptive Natural Density Filter.

[0034] A support frame 44 a, 44 b extending from a base 46 provides aplatform upon which the laser light source structure 20, the motiontable 22 and detector structure 24 commonly connect. In this manner, theframe maintains a common reference point and distances and anglesbetween all structures are known or can be measured. In a preferredembodiment, the frame fixes the laser light source and detectorstructures relative to one another.

[0035] The apparatus 10 may additionally include variousmechanical/electrical interlocks (not shown) between any or all of theforegoing structures to meet or exceed federal safety requirements. Inone embodiment, the base 46, the frame 44 and all structures connectedthereto reside within a light safe enclosure (not shown) according toANSI standard Z136.1, for example. Other apparatus structures includesuitable power sources (not shown) to power some or all of theforegoing.

[0036] During use, the apparatus 10 works to emanate and project a laserbeam(s) along the optical path from the laser light source structure 20to a front side 52 of the work piece. In turn, the laser beam(s) passes,or not, through the work piece 50 to a backside 54 and into thedetector. Signals output from the detector become transferred to thecomputing system environment where a user/software analyzes them forlight transmissivity characteristics of the work piece.

[0037] More specifically, and as a preliminary matter, the work piece 50is loaded in the tray 70 at a home position, which is around 200 mm awayfrom the laser light source structure 20 and the detector structure 24.A safety door of the light safe enclosure shuts and the apparatusobtains a baseline measurement reading by originating and projecting alaser beam along the optical path in a direct line from the light sourcestructure to the detector structure without passing the laser beamthrough the work piece.

[0038] Thereafter, the work piece 50 is inserted into the optical pathby movement from the home position to a starting position between thelaser light source and detector structures by the X-Y motion table. Thelaser beam projects toward/through the work piece and light collectedfrom the backside 54 by the detector corresponds to a work piecemeasurement reading. This process repeats, as described in greaterdetail below, such that pluralities of work piece measurement readingsare obtained. Differences between the baseline measurement and the workpiece measurement readings reveal the laser light transmissivity of thework piece. In a preferred embodiment, voltage outputs of the detectorstructure 24 have a mathematical relationship in terms of transmittedlight T(t) such that T(t)=Y(t)/X; where Y is the detected intensity attime t and X is the baseline measurement reading. A mean transmissivityvalue can be calculated by summing the above equation for the durationof a given time interval.

[0039] As an example, consider a baseline measurement reading havingsome trivial output of about 10 volts. Next consider a first work piecemeasurement reading of about 7 volts. In percentages, the laser lighttransmissivity of the work piece at that work piece position is about70%. Then, as additional work piece measurement readings are taken,preferably at other work piece positions, information about the workpiece transmissivity is obtained and can be graphed as shownrepresentatively in FIG. 4.

[0040] As readily identifiable in the graph, laser light transmissivitypreferably stays within a zone B between 50 and 100 percent, forexample. Yet, at measurement positions 1000 and 4000, laser lighttransmissivity drops to much lower percentage levels. Over time, andfrom knowledge learned by testing and identifying acceptable laser weldsof work pieces, users can set some minimum acceptable level, such asdashed line 60, that readily identifies whether the work piece undertest in apparatus 10 will yield satisfactory weld results. Users willset their own criteria for distinguishing satisfactory welds fromunsatisfactory ones. The criteria may include, but are not limited to,how many aberrations such as those found at positions 1000/4000 a weldcan withstand or how high a laser light transmissivity percentage onaverage, total, or other will yield an acceptable result. For thoroughdisclosure, the representative readings taken at work piece measurementpositions 1000 and 4000 were found in one actual reduction to practiceto correspond to impurities, such as carbon or steel, in the compositionof the work piece in instances when the work piece comprised a plasticformed in an injection molding chamber.

[0041] It should be appreciated, however, that testing the work piece inapparatus 10 (FIG. 1) for transmissivity characteristics is performed ata laser wavelength corresponding substantially to the specific laserwavelength used during laser welding. Even more preferably, testing ofthe work pieces in apparatus 10 occurs with the same exact laser lightsource structure 20 used during subsequent laser welding operations ofthe work piece. In this manner, users can even more accurately predictand identify a direct correlation between transmissivity andsatisfactory welds.

[0042] To physically introduce the work piece between the laser lightsource and detector structures, the offset arm 34 having the work piece50 therewith rotates or otherwise moves into the optical path. Withreference to FIGS. 2A and 2B, a preferred structure for holding the workpiece at a terminal end of the offset arm includes a tray 70.

[0043] As shown, the tray 70 has a plurality of walls 72(a-d) that forma frame around a periphery 56 of the work piece 50. A perimeter distanceof an interior 74 of the walls is slightly larger than the perimeterdistance of the periphery 56. In this manner, a user may easily insertthe work piece into the tray and the tray will maintain the work piecein a fixed position relative thereto. Near a bottom 75(a-d) of thewalls, a ledge 76(a-d) juts out slightly such that when the work pieceis inserted into the tray, the front side 52 surface of the work piecerests in contact on a top surface 80(a-d) thereof. In one embodiment,the ledge juts out a distance d of about {fraction (5/1000)}^(th) of aninch.

[0044] Those skilled in the art should observe that despite a slightledge, the tray otherwise has a substantially bottomless quality. Inthis manner, when the laser light source structure 20 (FIG. 1) projectslaser beams of light towards, and perhaps through the work piece, thesubstantially bottomless tray 70 suspends the work piece between thelaser light source and detector structures such that nearly the entiretyof the front side 52 surface of the work piece receives direct laserlight without any interference from the tray. Preferably, in a directline (e.g., optical path, dashed line, FIG. 1) between the laser lightsource structure 20 and the detector structure 24, no portion of thetray ever crosses the line.

[0045] The tray 70 can affix to the offset arm at any variety ofpositions, such as outside 73 of wall 72 a, by adhesives, clamps,fasteners or other or by integral formation therewith.

[0046] As depicted, the work piece 50 has a thickness t less than aheight h of the walls so that it nests within the tray. Those skilled inthe art will appreciate, however, that the work piece may have otherthicknesses that extend beyond or exist substantially parallel to a top82(a-d) of the walls and this invention embraces all varieties.

[0047] To have even greater usefulness, the positions, in whichtransmissivity measurements are taken, should correspond directly to thepositions that will later become laser welded. With reference to FIG.2C, a plurality of such later-welded work piece positions are showngenerally as a plurality of discrete dots (with two labeled 90-1 and90-4) arranged in a substantially rectangular pattern (although onlyshown on three sides of the work piece 50 with a dashed line arrow Cindicating continuation of the pattern) substantially paralleling aperiphery 56 of the work piece. Thus, when users take measurements theydo so at the positions indicated by the pattern.

[0048] The invention, however, should not be considered so narrowly topreclude other patterns of work piece positions. Thus, the inventioncontemplates other patterns and user need generally dictates them. Forexample, the invention finds equal utility with round, triangular,square, linear, spotted and random or other patterns or patterns ofcontinual lines of positions instead of discrete positions orcombinations thereof.

[0049] In one actual embodiment, the invention found utility with about12,000 work piece positions in a substantially rectangular pattern withabout ½ of {fraction (1/1000)}^(th) of an inch between positions. Themeasurements occurred at the work piece positions in the followingmanner: i) introduce and suspend the work piece in the tray at a homeposition away from the optical path; ii) project a laser beam directlyfrom the light source to the detector structure; iii) obtain a baselinemeasurement reading; (iv) energize stepping motor to stepwise controlmovement of the tray and work piece to the starting position between thelight source and detector structures directly in the optical path; v)obtain a work piece measurement reading by passing the laser beam (whichis continuous on, but not necessarily required to be) from the lightsource structure into the work piece and observing/recording the outputof the detector structure; (vi) energize the stepping motor to stepwisecontrol movement of the tray; (vii) index the tray 70 and work piece 50such that the next work piece position is in the optical path; (viii)repeat steps (v)-(viii) until an entirety of the work piece is measured;ix) stop the laser beam from projecting; and x) return tray 70 and workpiece to the home position by indexing the stepping motor. The workpiece embodied a substantially rectangular solid plastic composition ofNoryl Brand TN 300 having a thickness of about 2 mm and a length andwidth of about 50 mm and 25 mm, respectively.

[0050] With reference to FIG. 3, the invention presents a more detailedillustration of a preferred optical path for use in the apparatus 10 ofFIG. 1. In particular, laser diode 28 in combination with a collimatinglens 100 and focusing lens 102 projects a laser beam 104 from the laserlight source structure towards a front side 52 of the work piece 50. Thedetector structure collects transmitted laser light 106 from a back side54 of the work piece with assistance from a converging lens 108, filter42 and photodetector 40. In other embodiments, the optical pathoptionally includes additional lenses, filters collimators or otheroptical elements, such as mirrors, fiber optic strands, scanningstructures or the like.

[0051] Finally, since the invention herein contemplates the work pieceas an ink-jet printhead lid or body, the remaining description relatesto specific work piece compositions and their arrangement as part of alaser welded printhead lid/body.

[0052] With reference to FIG. 5, a printhead of the present invention isshown generally as 101. The printhead 101 has a housing 121 formed of abody 161 and a lid 160 laser welded together by a laser beam at awelding laser wavelength at a specific work piece position at a timeafter the lid has its work piece position measured for laser lighttransmissivity at the specified welding laser wavelength. In onepreferred embodiment, the lid comprises a laser transparent materialhaving a composition of polyphenylene ether plus polystyrene while thebody comprises a laser absorbing material also having a composition ofpolyphenylene ether plus polystyrene. Although shown generally as arectangular solid, the housing shape varies and depends upon theexternal device that carries or contains the printhead. The housing hasat least one compartment, internal thereto, for holding an initial orrefillable supply of ink and a structure, such as a foam insert, lung orother, for maintaining appropriate backpressure in the inkjet printheadduring use. In one embodiment, the internal compartment includes threechambers for containing three supplies of ink, especially cyan, magentaand yellow ink. In other embodiments, the compartment may contain blackink, photo-ink and/or plurals of cyan, magenta or yellow ink. It will beappreciated that fluid connections (not shown) may exist to connect thecompartment(s) to a remote source of ink.

[0053] A portion 191 of a tape automated bond (TAB) circuit 201 adheresto one surface 181 of the housing while another portion 211 adheres toanother surface 221. As shown, the two surfaces 181, 221 existperpendicularly to one another about an edge 231.

[0054] The TAB circuit 201 has a plurality of input/output (I/O)connectors 241 fabricated thereon for electrically connecting a heaterchip 251 to an external device, such as a printer, fax machine, copier,photo-printer, plotter, all-in-one, etc., during use. Pluralities ofelectrical conductors 261 exist on the TAB circuit 201 to electricallyconnect and short the I/O connectors 241 to the bond pads 281 of theheater chip 251 and various manufacturing techniques are known forfacilitating such connections. It will be appreciated that while eightI/O connectors 241, eight electrical conductors 261 and eight bond pads281 are shown, any number are embraced herein. It is also to beappreciated that such number of connectors, conductors and bond pads maynot be equal to one another.

[0055] The heater chip 251 contains at least one ink via 321 thatfluidly connects to a supply of ink internal to the housing. Duringprinthead manufacturing, the heater chip 251 preferably attaches to thehousing with any of a variety of adhesives, epoxies, etc. well known inthe art. As shown, the heater chip contains two columns of heaters oneither side of via 321. For simplicity in this crowded figure, dotsdepict the heaters in the columns. It will be appreciated that theheaters of the heater chip preferably become formed as a series of thinfilm layers made via growth, deposition, masking, photolithographyand/or etching or other processing steps. A nozzle plate withpluralities of nozzle holes, not shown, adheres over the heater chipsuch that the nozzle holes align with the heaters.

[0056] With reference to FIG. 6, an external device, in the form of aninkjet printer, for containing the printhead 101 is shown generally as401. The printer 401 includes a carriage 421 having a plurality of slots441 for containing one or more printheads. The carriage 421 is caused toreciprocate (via an output 591 of a controller 571) along a shaft 481above a print zone 461 by a motive force supplied to a drive belt 501 asis well known in the art. The reciprocation of the carriage 421 isperformed relative to a print medium, such as a sheet of paper 521, thatis advanced in the printer 401 along a paper path from an input tray541, through the print zone 461, to an output tray 561.

[0057] In the print zone, the carriage 421 reciprocates in theReciprocating Direction generally perpendicularly to the paper AdvanceDirection as shown by the arrows. Ink drops from the printheads (FIG. 5)are caused to be ejected from the heater chip at such times pursuant tocommands of a printer microprocessor or other controller 571. The timingof the ink drop emissions corresponds to a pattern of pixels of theimage being printed. Often times, such patterns are generated in deviceselectrically connected to the controller (via Ext. input) that areexternal to the printer such as a computer, a scanner, a camera, avisual display unit, a personal data assistant, or other.

[0058] To print or emit a single drop of ink, the heaters (the dots ofFIG. 5) are uniquely addressed with a small amount of current to rapidlyheat a small volume of ink. This causes the ink to vaporize in a localink chamber and be ejected through, and projected by, a nozzle platetowards the print medium.

[0059] A control panel 581 having user selection interface 601 may alsoprovide input 621 to the controller 571 to enable additional printercapabilities and robustness.

[0060] As described herein, the term inkjet printhead may in addition tothermal technology include piezoelectric technology, or other, and mayembody a side-shooter structure instead of the head-shooter structureshown. Finally, since the to-be-welded work piece described above mayembody an inkjet printhead lid and/or body and since laser weldingimparts essentially no vibratory motion in the work pieces, unlikeultrasonic welding, less cracking of the heater chip occurs and less airbecomes entrained in the ink during printhead manufacturing.

[0061] The foregoing description is presented for purposes ofillustration and description of the various aspects of the invention.The descriptions are not intended to be exhaustive or to limit theinvention to the precise form disclosed. The embodiments described abovewere chosen to provide the best illustration of the principles of theinvention and its practical application to thereby enable one ofordinary skill in the art to utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. All such modifications and variations arewithin the scope of the invention as determined by the appended claimswhen interpreted in accordance with the breadth to which they arefairly, legally and equitably entitled.

What is claimed is:
 1. A method for measuring laser lighttransmissivity, comprising: introducing a work piece that is to undergolaser welding at a specific laser wavelength at a work piece positionbetween a laser light source and a detector; passing a laser beam atsaid wavelength from said laser light source through said work piece ina vicinity of said work piece position and into said detector to obtaina work piece measurement reading; based upon said reading, assessingwhether said work piece will satisfactorily undergo laser welding atsaid work piece position at said wavelength.
 2. The method of claim 1,further including stepwise controlling movement of said work piecebetween said laser light source and said detector through a plurality ofpositions.
 3. The method of claim 1, further including projecting saidlaser beam at said wavelength from said laser light source into saiddetector without passing through said work piece to obtain a baselinemeasurement reading.
 4. The method of claim 3, further includingdetermining a difference between said baseline measurement reading andsaid work piece measurement reading.
 5. The method of claim 1, whereinsaid introducing further includes suspending said work piece in asubstantially bottomless tray.
 6. The method of claim 1, furtherincluding laser welding said work piece to an ink-jet printhead body atsaid work piece position.
 7. A method for measuring laser lighttransmissivity in a work piece, comprising: providing a work piece thatundergoes laser welding at a specific laser wavelength at a work pieceposition; providing a laser light source and a detector; projecting alaser beam at said wavelength from said laser light source into saiddetector to obtain a baseline measurement reading; thereafter,suspending said work piece between said laser light source and saiddetector; projecting said laser beam at said wavelength from said laserlight source through said work piece in a vicinity of said work pieceposition and into said detector to obtain a work piece measurementreading; determining a difference between said work piece measurementreading and said baseline measurement reading; and based upon saiddetermining a difference, identifying whether said work piece willsatisfactorily undergo laser welding at said work piece position at saidwavelength.
 8. The method of claim 7, wherein said suspending furtherincludes framing said work piece in a substantially bottomless tray suchthat, in a direct line between said laser light source and saiddetector, no portion of said tray crosses said line.
 9. The method ofclaim 7, further including stopping said projecting said laser beam andindexing said work piece.
 10. The method of claim 7, further includingprojecting said laser beam at said wavelength from said laser lightsource through said work piece in a vicinity of a second work pieceposition and into said detector to obtain a second work piecemeasurement reading.
 11. The method of claim 10, further includingdetermining a difference between said second work piece measurementreading and said baseline measurement reading.
 12. The method of claim11, based upon said determining a difference between said second workpiece measurement reading and said baseline measurement reading,identifying whether said work piece will satisfactorily undergo laserwelding at said second work piece position at said wavelength.
 13. Themethod of claim 7, further including laser welding said work piece to anink-jet printhead body at said work piece position.
 14. A method formeasuring laser light transmissivity of a work piece, comprising:providing a work piece that undergoes laser welding at a specific laserwavelength at a plurality of work piece positions; fixing a position ofa laser light source and a detector relative to one another; suspendingsaid work piece at a home position, said suspending including framingsaid work piece in a substantially bottomless tray such that, in adirect line between said laser light source and said detector, noportion of said tray crosses said line; with said work piece at saidhome position, projecting a laser beam at said wavelength from saidlaser light source into said detector to obtain a baseline measurementreading; moving said work piece from said home position to a first ofsaid plurality of work piece positions, said work piece at said first ofsaid plurality of work piece positions crossing said direct line;thereafter, projecting said laser beam at said wavelength from saidlaser light source through said work piece at said first of saidplurality of work piece positions and into said detector to obtain afirst work piece measurement reading; indexing said tray; projectingsaid laser beam at said wavelength from said laser light source throughsaid work piece at a second of said plurality of work piece positionsand into said detector to obtain a second work piece measurementreading; determining a difference between each of said first and secondwork piece measurement readings and said baseline measurement reading;and based upon said determining a difference, identifying whether saidwork piece will satisfactorily undergo laser welding at said first andsecond work piece positions at said wavelength.
 15. The method of claim14, further including laser welding said work piece to an ink-jetprinthead body at said first and second work piece positions.
 16. Themethod of claim 14, wherein said indexing further includes stepping saidtray in a pattern substantially paralleling a periphery of said workpiece.
 17. The method of claim 14, wherein said suspending furtherincludes laying a surface of said work piece onto a ledge of saidsubstantially bottomless tray.
 18. An inkjet printhead, comprising: aninkjet printhead body; and an inkjet printhead lid having at least onework piece position thereof measured for laser light transmissivity at aspecific laser wavelength laser welded to said ink-jet printhead body atsaid at least one work piece position.
 19. The inkjet printhead of claim18, wherein said inkjet printhead lid further includes a plurality ofwork piece positions measured for laser light transmissivity at saidwavelength arranged in a pattern substantially paralleling a peripheryof said work piece.
 20. The inkjet printhead of claim 19, wherein saidpattern is substantially rectangular.